1. Field
The invention is in the field of high brightness laser systems which use a low energy master oscillator laser beam and a power amplifier usually limited to a low pulse repetition rate, and specifically to the time-multiplexing of a plurality of phase conjugated power amplifiers in which the oscillator laser beam pulses pass through an optical diode comprised of a polarizer, a half-wave plate, and a Faraday rotator and wherein a plurality of Pockels cells are electronically sequentially switched to divert successive oscillator pulses to sequential amplifiers in a Gatling gun fashion of firing the amplifiers and out the optical diode to provide a high pulse repetition rate for the laser system.
2. Prior Art
Known high brightness lasers which use solid state lasers as power amplifiers in a laser oscillator system are usually pulse rate limited by the thermal effects in the power amplifier laser rods. The pulse repetition frequency may be limited to about 60 Hertz. A laser system which is limited in frequency is a laser oscillator and a solid state laser rod phase conjugated power amplifier with a polarizer in optical alignment therebetween for routing the oscillator laser beam pulses into the phase conjugated power amplifier and the retroreflected amplified output laser beam pulses out of the laser system toward a target. The phase conjugated power amplifier has at the back side a quarter-wave plate and a phase conjugate mirror, comprised of a focusing lens and a stimulated Brillouin scattering cell, for retroreflecting the once amplified beam back. The retroreflected beam is amplified a second time then on the pass back through the power amplifier. The two passes through the quarter-wave plate result in the beam polarization to rotate by 90.degree.. The twice amplified output beam pulse is reflected off the polarizer.
The stimulated Brillouin scattering of the laser beam pulses results in a phase conjugated and distortion free retroreturn of the input laser beam pulse even when the amplifier has some slight movement or misalignment. Such a laser system has high-fidelity amplification and a stable output beam direction. The frequency of producing laser pulses therefrom is however limited by the temperature generated in the laser rods of the power amplifiers.
The present invention provides an increased pulse repetition frequency by switching a plurality of phase conjugate amplifiers sequentially in sychronism with the oscillator laser beam pulses so that no amplifier is overloaded. The amplifiers are the solid state laser rod type with each having an input thereto along an optical axis of a laser oscillator and an output therefrom to a phase conjugate mirror which retroflects the pulse back through the quarter-wave plate. The phase conjugate mirror is comprised of a focusing lens and a stimulated Brillouin scattering cell. The amplifiers are selectively time multiplexed sequentially with the input beam pulses so that each individual amplifier unit operates at a frequency below the critical overheating level, which may be at about 60 Hertz. By use of the stimulated Brillouin scattering cell for retroreflection, the outputs from each amplifier is automatically and stably aligned with the outputs of the other amplifiers.
A similar patent application is concurrently filed, titled "Gatling Gun Laser Amplifier Using Rotating Mirrors" by co-inventors Suresh Chandra and Geraldine Daunt. The other application is however distinctly different from the present invention.